Projection lens and projection-type display apparatus using the lens

ABSTRACT

A projection lens is composed of a positive first lens group, a negative second lens group, and a positive third lens group, which are sequentially arranged from the magnification side of the projection lens, and the reduction side of the projection lens is telecentric. Further, the following formulas (1) and (2) are satisfied:
 
0.30≦ d   23   /f   3 ≦0.65  (1); and
 
10≦| D   12   /ff|   (2), where
         d 23 : space in air between the second lens group and the third lens group,   f 3 : focal length of the third lens group,   D 12 : total length of the first lens group and the second lens group in the direction of an optical axis, and   ff: length from the most magnification-side surface in the entire system of the projection lens to a magnification-side focus position of the entire system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projection lens to be mounted on aprojection-type display apparatus, and the projection-type displayapparatus. Particularly, the present invention relates to a projectionlens appropriate for a small projector apparatus on which a light valve,such as a transmissive liquid crystal panel, a reflective liquid crystalpanel and a DMD (digital micromirror device), is mounted, and to theprojector apparatus.

2. Description of the Related Art

As projectors rapidly spread, and became widely used in recent years, ademand for small projectors that are light-weight and low-price, andwhich are conveniently usable and easily settable, increased. To satisfysuch a demand, projections lenses for the projectors also need to besmall, light-weight and low-price.

When the back focus of a projection lens is reduced, it is possible toreduce the outer diameter of a reduction-side lens in the projectionlens. As such a projection lens, lenses disclosed in Japanese Patent No.4164283 (Patent Document 1) and Japanese Unexamined Patent PublicationNo. 2005-215310 (Patent Document 2) are known.

In the projection lenses disclosed in Patent Documents 1 and 2, theouter diameters of the reduction-side lenses can be reduced. However,the number of lenses is 10 or 11, which is many, and the total length istoo long. Further, in Patent Documents 1 and 2, an increase in the outerdiameter of a magnification-side lens is not considered. Therefore, thesize of the entire lens system is not sufficiently reduced.

SUMMARY OF THE INVENTION

In view of the foregoing circumstances, it is an object of the presentinvention to provide a projection lens (a lens for projection) that canreduce the size of the lens system (compact lens system) by reducing thelength of the entire system and the outer diameter of at least onemagnification-side lens. Further, it is another object of the presentinvention to provide a projection-type display apparatus using theprojection lens.

A projection lens of the present invention is a projection lenscomprising:

a first lens group having positive refractive power;

a second lens group having negative refractive power; and

a third lens group having positive refractive power, which aresequentially arranged from the magnification side of the projectionlens,

wherein the reduction side of the projection lens is telecentric, and

wherein the following formulas (1) and (2) are satisfied:0.30≦d ₂₃ /f ₃≦0.65  (1); and10≦|D ₁₂ /ff|  (2), where

d₂₃: space in air between the second lens group and the third lensgroup,

f₃: focal length of the third lens group,

D₁₂: total length of the first lens group and the second lens group inthe direction of an optical axis, and

ff: length from the most magnification-side surface in the entire systemof the projection lens to a magnification-side focus position of theentire system.

Further, it is desirable that the following formula (3) is satisfied:bf/f ₃≦0.2  (3), where

bf: back focus in air of the entire system.

Further, it is desirable that the following formula (4) is satisfied:1.2≦f ₃ /f≦1.9  (4), where

f: focal length of the entire system.

Further, it is desirable that the following formula (5) is satisfied:0.4≦D ₁₂ /f ₃≦1.1  (5).

Further, it is desirable that the following formula (6) is satisfied:0.2≦f ₁ /f≦1.0  (6), where

f₁: focal length of the first lens group.

Further, it is desirable that the following formula (7) is satisfied:−3.5≦f ₂ /f≦−0.5  (7), where

f₂: focal length of the second lens group.

Further, it is desirable that the first lens group is composed ofnegative lens G₁₁, positive lens G₁₂ and positive lens G₁₃, which aresequentially arranged from the magnification side of the projectionlens, or the first lens group is composed of negative lens G₁₁ andpositive lens G₁₂, which are sequentially arranged from themagnification side of the projection lens.

Further, it is desirable that the second lens group is composed ofnegative lens G₂₁ and positive lens G₂₂, which are sequentially arrangedfrom the magnification side of the projection lens.

Further, it is desirable that the third lens group consists of positivelens G₃₁.

Further, it is desirable that illumination light and projection lightare separated from each other in an area between the second lens groupand the third lens group.

Further, it is desirable that rays from a plurality of light valves arecombined together in an area between the second lens group and the thirdlens group.

Further, it is desirable that a stop is arranged on the magnificationside of the first lens group.

A projection-type display apparatus of the present invention is aprojection-type display apparatus comprising:

a light source;

a light valve;

an illumination optical unit that guides rays of light from the lightsource to the light valve; and

a projection lens according to one of aspects of the present invention,

wherein the rays of light from the light source are optically modulatedby the light valve and projected onto a screen by the projection lens.

Here, the term “magnification side” refers to a side (screen side) ontowhich an image or the like is projected. In reduction projection, thescreen side is also referred to as the magnification side, forconvenience. Further, the term “reduction side” refers to an originalimage display area side (light valve side). In reduction projection, thelight valve side is also referred to as the reduction side, forconvenience.

In a projection lens of the present invention and a projection-typedisplay apparatus of the present invention using the projection lens,the projection lens is composed of three groups of a positive lensgroup, a negative lens group and a positive lens group. Further, theprojection lens is structures so as to satisfy the aforementionedformulas (1) and (2).

The projection lens of the present invention and the projection-typedisplay apparatus of the present invention using the projection lenssatisfy the formula (1), as described. Therefore, it is possible toprevent the length of the entire system from becoming too long, whilestructuring the projection lens in such a manner that a ray separationoptical system, a ray combination optical system, or the like isinsertable in an area between the second lens group and the third lensgroup. The ray separation optical system separates illumination lightand projection light from each other, and the ray combination opticalsystem combines rays from plural modulation elements together.Specifically, in the projection lens of the present invention, a spacefor inserting an optical prism is provided between the second lens groupand the third lens group in the lens system. Further, the projectionlens of the present invention is structured so that a light valve isarrangeable without leaving a substantial space on the reduction side ofthe lens system. Therefore, it is possible to reduce the outer diameterof at least one reduction-side lens in the projection lens.

Further, since the projection lens of the present invention satisfiesthe formula (2), it is possible to reduce the outer diameter of at leastone magnification-side lens in the projection lens, while the reductionside of the lens system is kept telecentric. In other words, when theformula (2) is satisfied, it is possible to limit the sum of the lengthof the first lens group and the length of the second lens group.Further, since the upper limit of d₂₃/f₃ is defined by the formula (1),it is possible to reduce the length of the entire lens, and to reducethe size of the projection lens. Further, when the formula (2) issatisfied, length ff from the most-magnification-side surface in theentire system to the magnification-side focus position of the entiresystem is extremely short. Further, since the reduction side of the lenssystem is telecentric, a front-side focus position, at which rayscondense most, is located in the vicinity of a magnification-side lens.Therefore, it is possible to solve the problem in conventionaltechniques that the external diameter of the magnification-side lensshould be reduced. Further, it is possible to reduce the size of theentire lens system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the structure of a projection lens inExample 1;

FIG. 2 is a diagram illustrating the structure of a projection lens inExample 2;

FIG. 3 is a diagram illustrating the structure of a projection lens inExample 3;

FIG. 4 is a diagram illustrating the structure of a projection lens inExample 4;

FIG. 5 is a diagram illustrating the structure of a projection lens inExample 5;

FIG. 6 is a diagram illustrating the structure of a projection lens inExample 6;

FIG. 7-i is a diagram illustrating the spherical aberration of theprojection lens in Example 1 (72.0 times magnification);

FIG. 7-ii is a diagram illustrating the astigmatism of the projectionlens in Example 1 (72.0 times magnification);

FIG. 7-iii is a diagram illustrating the distortion of the projectionlens in Example 1 (72.0 times magnification);

FIG. 7-iv is a diagram illustrating the lateral chromatic aberration ofthe projection lens in Example 1 (72.0 times magnification);

FIG. 8-i is a diagram illustrating the spherical aberration of theprojection lens in Example 2 (72.0 times magnification);

FIG. 8-ii is a diagram illustrating the astigmatism of the projectionlens in Example 2 (72.0 times magnification);

FIG. 8-iii is a diagram illustrating the distortion of the projectionlens in Example 2 (72.0 times magnification);

FIG. 8-iv is a diagram illustrating the lateral chromatic aberration ofthe projection lens in Example 2 (72.0 times magnification);

FIG. 9-i is a diagram illustrating the spherical aberration of theprojection lens in Example 3 (72.0 times magnification);

FIG. 9-ii is a diagram illustrating the astigmatism of the projectionlens in Example 3 (72.0 times magnification);

FIG. 9-iii is a diagram illustrating the distortion of the projectionlens in Example 3 (72.0 times magnification);

FIG. 9-iv is a diagram illustrating the lateral chromatic aberration ofthe projection lens in Example 3 (72.0 times magnification);

FIG. 10-i is a diagram illustrating the spherical aberration of theprojection lens in Example 4 (72.0 times magnification);

FIG. 10-ii is a diagram illustrating the astigmatism of the projectionlens in Example 4 (72.0 times magnification);

FIG. 10-iii is a diagram illustrating the distortion of the projectionlens in Example 4 (72.0 times magnification);

FIG. 10-iv is a diagram illustrating the lateral chromatic aberration ofthe projection lens in Example 4 (72.0 times magnification);

FIG. 11-i is a diagram illustrating the spherical aberration of theprojection lens in Example 5 (72.0 times magnification);

FIG. 11-ii is a diagram illustrating the astigmatism of the projectionlens in Example 5 (72.0 times magnification);

FIG. 11-iii is a diagram illustrating the distortion of the projectionlens in Example 5 (72.0 times magnification);

FIG. 11-iv is a diagram illustrating the lateral chromatic aberration ofthe projection lens in Example 5 (72.0 times magnification);

FIG. 12-i is a diagram illustrating the spherical aberration of theprojection lens in Example 6 (72.0 times magnification);

FIG. 12-ii is a diagram illustrating the astigmatism of the projectionlens in Example 6 (72.0 times magnification);

FIG. 12-iii is a diagram illustrating the distortion of the projectionlens in Example 6 (72.0 times magnification);

FIG. 12-iv is a diagram illustrating the lateral chromatic aberration ofthe projection lens in Example 6 (72.0 times magnification);

FIG. 13 is a conceptual diagram of an optical system using atransmissive LCD panel (three panel type for RGB) and a cross dichroicprism in an embodiment of the present invention;

FIG. 14 is a conceptual diagram of an optical system using a reflectiveLCD panel (single panel type) and a PBS prism in an embodiment of thepresent invention;

FIG. 15 is a conceptual diagram of an optical system using a DMD displaypanel and a TIR prism in an embodiment of the present invention;

FIG. 16 is a conceptual diagram of an optical system using a DMD displaypanel and a mirror in an embodiment of the present invention; and

FIG. 17 is a schematic diagram illustrating the structure of aprojection-type display apparatus according to an embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to drawings. FIG. 1 is a diagram illustrating the basicstructure of a projection lens in Example 1 of the present invention.Embodiments of the present invention will be described using theprojection lens illustrated in FIG. 1 as an example.

The projection lens includes first lens group G₁ having positiverefractive power, second lens group G₂ having negative refractive power,and third lens group G₃ having positive refractive power, which aresequentially arranged from the magnification side of the projectionlens. Further, the reduction side of the projection lens is telecentric,and at least the following formulas (1) and (2) are satisfied:0.30≦d ₂₃ /f ₃≦0.65  (1); and10≦|D ₁₂ /ff|  (2), where

d₂₃: space in air between the second lens group G₂ and the third lensgroup G₃,

f₃: focal length of the third lens group G₃,

D₁₂: total length of the first lens group G₁ and the second lens groupG₂ in the direction of an optical axis, and

ff: length from the most magnification-side surface in the entire systemof the projection lens to a magnification-side focus position of theentire system.

The formula (1) represents the basic form of the projection lensaccording to the present embodiment, in which a space for inserting anoptical prism is provided between the second lens group G₂ and the thirdlens group G₃. When the formula (1) is satisfied, it is possible toprevent the length of the entire system from becoming too long, whilestructuring the projection lens in such a manner that a ray separationoptical system, a ray combination optical system, or the like isinsertable in a space between the second lens group G₂ and the thirdlens group G₃. The ray separation optical system separates illuminationlight and projection light from each other, and the ray combinationoptical system combines rays from plural modulation elements together.Further, since the back side of the third lens group G₃ can be reduced,it is possible to reduce the external diameter of at least onereduction-side lens. When the value of d₂₃/f₃ exceeds the upper limitdefined by the formula (1), the length of the entire lens system becomestoo long. When the value of d₂₃/f₃ is lower than lower limit defined bythe formula (1), it becomes difficult to insert the ray separationoptical system for separating illumination light and projection lightfrom each other, the ray combination optical system for combining raysfrom plural modulation elements together, or the like.

Therefore, it is desirable that the following formula (1′) is satisfiedinstead of the formula (1):0.30≦d ₂₃ /f ₃≦0.55  (1′).

Further, when the formula (2) is satisfied, length ff from themost-magnification-side surface in the entire system to themagnification-side focus position of the entire system is extremelyshort. Further, since the reduction side of the lens system istelecentric, a front-side focus position, at which rays condense most,is located in the vicinity of a magnification-side lens. Therefore, whenthe formula (2) is satisfied, it is possible to reduce the externaldiameter of at least one magnification-side lens. Hence, it is possibleto reduce the size of the entire lens system. Further, when the formula(2) is satisfied, the sum of the length of the first lens group G₁ andthe length of the second lens group G₂ is suppressed. Therefore, it ispossible to reduce the length of the entire lens system. Accordingly, itis possible to reduce the size of the entire lens system (compact lenssystem).

Therefore, it is more desirable that the following formula (2′) issatisfied instead of the formula (2), and it is even more desirable thatthe following formula (2″) is satisfied:15≦|D ₁₂ /ff|  (2′); where30≦|D ₁₂ /ff|  (2″).

Further, it is desirable that the first lens group G₁ is composed ofnegative lens G₁₁ (first lens L₁), positive lens G₁₂ (second lens L₂),and positive lens G₁₃ (third lens L₃), which are sequentially arrangedfrom the magnification side (please refer to Examples 1, 2, 4 and 5).Alternatively, it is desirable that the first lens group G₁ is composedof negative lens G₁₁ (first lens L₁) and positive lens G₁₂ (second lensL₂), which are sequentially arranged from the magnification side (pleaserefer to Examples 3 and 6).

Further, it is desirable that the second lens group G₂ is composed ofnegative lens G₂₁ (fourth lens L₄ in Examples 1, 2, 4 and 5, and thirdlens L₃ in Examples 3 and 6) and positive lens G₂₂ (fifth lens L₅ inExamples 1, 2, 4 and 5, and fourth lens L₄ in Examples 3 and 6).

Further, it is desirable that the third lens group G₃ consists ofpositive lens G₃₁, in other words, the third lens group G₃ is composedof only positive lens G₃₁ (sixth lens L₆ in Examples 1, 2, 4 and 5, andfifth lens L₅ in Examples 3 and 6).

Further, it is desirable that illumination light and projection lightare separated from each other, or rays from plural spatial modulationelements are combined together in an area between the second lens groupG₂ and the third lens group G₃.

Further, it is desirable that a stop (or a mask) is arranged on themagnification side of the first lens group G₁. Alternatively, in thefirst lens group G₁, a spot (or a mask) may be arranged between themost-magnification-side lens (lens G₁₁) and a second lens from themagnification side (lens G₁₂).

Specific lens shape or the like will be described later in each example.

Further, a filter 1 a, such as an infrared-ray-cut filter or a low-passfilter, is arranged between the third lens group G₃ and an image displayplane 1. Further, a glass block (optical prism) 2 is arranged betweenthe second lens group G₂ and the third lens group G₃. The glass block 2corresponds to a ray separation optical system or a ray combinationoptical system. In FIG. 1, line Z represents an optical axis.

As the glass block (optical prism) 2 arranged between the second lensgroup G₂ and the third lens group G₃, various types of glass blockincluding those illustrated in FIGS. 13 through 16 may be used forexample.

Specifically, for example, as illustrated in FIG. 13, rays of light aremodulated by transmissive liquid crystal panels corresponding to lightof three colors, respectively. Further, rays of light of respectivecolors are output from image display planes 1B, 1G, and 1R of thetransmissive liquid crystal panels, respectively, and pass through thirdlens groups G₃ corresponding to the three colors, respectively. Afterthen, the rays of light of different colors are combined together by across dichroic prism 2 a, which is inserted between the third lensgroups G₃ and the second lens group G₂. The combined light passesthrough the second lens group G₂ and the first lens group G₁, and isprojected onto a screen, which is not illustrated.

Alternatively, for example, as illustrated in FIG. 14, a PBS prism 2 bmay be inserted between the third lens group G₃ and the second lensgroup G₂. The PBS prism 2 b deflects, toward the direction of imagedisplay plane 1P of a reflective liquid crystal display panel,illumination light entering from a direction perpendicular to opticalaxis Z. Further, the PBS prism 2 b passes modulation light output fromthe image display plane 1P of the reflective liquid crystal displaypanel straight along the optical axis Z. Accordingly, the PBS prism 2 bseparates the illumination light and the modulation light from eachother. The separated modulation light passes through the second lensgroup G₂ and the first lens group G₁, and is projected onto a screen,which is not illustrated.

Alternatively, for example, as illustrated in FIG. 15, a TIR prism 2 cmay be inserted between the third lens group G₃ and the second lensgroup G₂. The TIR prism 2 c deflects, toward the direction of imagedisplay plane 1Q of a DMD display panel, illumination light enteringfrom an oblique lower direction with respect to optical axis Z. Further,the TIR prism 2 c passes modulation light output from the image displayplane 1Q of the DMD display panel travel straight along the optical axisZ. Accordingly, the TIR prism 2 c separates the illumination light andthe modulation light from each other. The separated modulation lightpasses through the second lens group G₂ and the first lens group G₁, andis projected onto a screen, which is not illustrated.

Alternatively, for example, as illustrated in FIG. 16, a concave mirror2 d may be inserted, at a position away from optical axis Z, between thethird lens group G₃ and the second lens group G₂. The concave mirror 2 ddeflects, toward the direction of image display plane 1S of a DMDdisplay panel, illumination light entering from a directionperpendicular to the optical axis Z. Further, the concave mirror 2 dallows modulation light output from the image display plane 1S of theDMD display panel travel straight along the optical axis Z. Accordingly,the concave mirror 2 d separates the illumination light and themodulation light from each other. The separated modulation light passesthrough the second lens group G₂ and the first lens group G₁, and isprojected onto a screen, which is not illustrated.

Further, in the embodiments of the present invention, each asphericsurface is represented by the following equation:

$\begin{matrix}{{Z = {\frac{Y^{2}/R}{1 + \sqrt{1 - {K \times {Y^{2}/R^{2}}}}} + {\sum\limits_{i = 3}^{12}{A_{i}Y^{i}}}}},} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$where

Z: length of a perpendicular from a point on an aspheric surface, thepoint away from optical axis by distance Y, to flat plane (flat planeperpendicular to the optical axis) in contact with the vertex of theaspheric surface,

Y: distance from the optical axis,

R: curvature radius of the aspheric surface in the vicinity of theoptical axis,

K: eccentricity, and

A_(i): aspheric coefficient (i=3 through 12).

In the embodiments of the present invention, the formulas (1) and (2)are satisfied. Further, it is desirable that at least one of thefollowing formulas (3) through (7) is satisfied:bf/f ₃≦0.2  (3);1.2≦f ₃ /f≦1.9  (4);0.4≦D ₁₂ /f ₃≦1.1  (5);0.2≦f ₁ /f≦1.0  (6); and−3.5≦f ₂ /f≦−0.5  (7), where

bf: back focus in air of the entire system,

f: focal length of the entire system,

f₁: focal length of the first lens group G₁,

f₂: focal length of the second lens group G₂,

f₃: focal length of the third lens group G₃, and

D₁₂: the total length of the first lens group G₁ and the second lensgroup G₂ in the direction of the optical axis.

Next, the technical meanings of the formulas (3) through (7) will bedescribed.

The formula (3) defines the range of a value obtained by dividing theback focus bf in air of the entire system by focal length f₃ of thethird lens group G₃. The formula (3) defines the range for reducing thesize of the lens group G₃. In other words, when the value exceeds theupper limit defined by the formula (3), it becomes difficult to reducethe size of the third lens group G₃.

Therefore, it is more desirable that the following formula (3′) issatisfied instead of the formula (3):bf/f ₃≦0.15  (3′).

Further, the formula (4) defines the range of a value obtained bydividing the focal length f₃ of the third lens group G₃ by the focallength f of the entire system. The formula (4) defines a range in whichthe size of the second lens group G2 is reducible while correction ofaberration, such as image plane correction, is performed in an excellentmanner. In other words, when the value exceeds the upper limit definedby the formula (4), the total length of the second lens group G₂ becomestoo long, and it becomes difficult to reduce the size of the lenssystem. When the value is lower than the lower limit defined by theformula (4), the power of the third lens group G₃ becomes too strong,and it becomes difficult to perform correction of aberration, such asimage plane correction.

Therefore, it is more desirable that the following formula (4′) issatisfied instead of the formula (4):1.3≦f ₃ /f≦1.7  (4′).

Further, the formula (5) defines the range of a value obtained bydividing the total length D₁₂ of the first lens group G₁ and the secondlens group G₂ in the direction of the optical axis by the focal lengthf₃ of the third lens group G₃. When the formula (5) is satisfied, thetotal length D₁₂ of the first lens group G₁ and the second lens group G₂does not become too short, and aberrations are corrected in an excellentmanner. Further, the total length D₁₂ of the first lens group G₁ and thesecond lens group G₂ does not become too long. Therefore, it is possibleto reduce the size of the lens system. In other words, when the valueexceeds the upper limit defined by the formula (5), the total length ofthe first lens group G₁ and the second lens group G₂ becomes too long.Further, when the value is lower than the lower limit defined by theformula (5), the total length of the first lens group G₁ and the secondlens group G₂ becomes too short, and it becomes difficult to performcorrection of aberration, such as image plane correction.

Therefore, it is desirable that the following formula (5′) is satisfiedinstead of the formula (5):0.5≦D ₁₂ /f ₃≦0.9  (5′).

Further, the formula (6) defines the range of a value obtained bydividing the focal length f₁ of the first lens group G₁ by the focallength f of the entire system. The formula (6) defines a range in whichthe size of the first lens group G₁ is reducible while chromaticaberration is corrected in an excellent manner. In other words, when thevalue exceeds the upper limit defined by the formula (6), the totallength of the first lens group G₁ becomes too long, and it becomesdifficult to reduce the size of the entire system. When the value islower than the lower limit defined by the formula (6), the power of thefirst lens group G₁ becomes too strong, and it becomes difficult tocorrect aberrations, such as chromatic aberration.

Therefore, it is more desirable that the following formula (6′) issatisfied instead of the formula (6), and it is even more desirable thatthe following formula (6″) is satisfied:0.3≦f ₁ /f≦0.8  (6′); and0.4≦f ₁ /f≦0.7  (6″).

Further, the formula (7) defines the range of a value obtained bydividing the focal length f₂ of the second lens group G₂ by the focallength f of the entire system. The formula (7) defines a range in whichthe size of the second lens group G₂ is reducible while various kinds ofaberration are corrected in an excellent manner. In other words, whenthe value exceeds the upper limit defined by the formula (7), the powerof the second lens group G₂ becomes too strong, and it becomes difficultto correct various kinds of aberration. When the value is lower than thelower limit defined by the formula (7), the total length of the secondlens group G₂ becomes too long, and it becomes difficult to reduce sizeof the entire system.

Therefore, it is desirable that the following formula (7′) is satisfiedinstead of the formula (7), and it is more desirable that the followingformula (7″) is satisfied:−3.0≦f ₂ /f≦−0.7  (7′); and−2.5≦f ₂ /f≦−0.8  (7″).

Next, with reference to FIG. 17, an example of a projection-type displayapparatus on which the projection lens of the present invention ismounted will be described. A projection-type display apparatus 30illustrated in FIG. 17 includes transmissive liquid crystal panels 11 athrough 11 c, as light valves. Further, the projection-type displayapparatus 30 uses, as a projection lens 10, a projection lens accordingto the aforementioned embodiments of the present invention. In FIG. 17,a light source 15 and a dichroic mirror 12 are not illustrated. Whitelight is output from the light source 15, and enters, through anillumination optical unit, liquid crystal panels 11 a through 11 c,which correspond to rays of light of three colors (G light, B light andR light), respectively, and is optically modulated. The modulated raysof light are combined together by the cross dichroic prism 14, andprojected by the projection lens 10 onto a screen, which is notillustrated. Further, the projection-type display apparatus 30 includescondenser lenses 16 a through 16 c and total reflection mirrors 18 athrough 18 c.

The projection-type display apparatus 30 according to an embodiment ofthe present invention uses the projection lens in which the size of theentire system has been reduced. Therefore, it is possible to reduce thewhole size of the projection-type display apparatus 30.

It is not necessary that the projection lens of the present inventionuses, as light valves, transmissive liquid crystal display panels. Theprojection lens of the present invention may be used, as a projectionlens, in a apparatus using a reflective liquid crystal display panel orother optical modulation means, such as a DMD.

EXAMPLES

Next, examples of the present invention will be specifically describedby using data.

Example 1

A projection lens in Example 1 is structured as illustrated in FIG. 1.Specifically, the projection lens is composed of first lens group G₁,second lens group G₂, and third lens group G₃, which are sequentiallyarranged from the magnification side of the projection lens. The firstlens group G₁ is composed of first lens L₁, second lens L₂ and thirdlens L₃, which are sequentially arranged from the magnification side.Both surfaces of the first lens L₁ are aspheric (double concave(concave-concave) in the vicinity of the optical axis), and the firstlens L₁ is made of plastic. The second lens L₂ is a double convex(convex-convex) lens made of glass. The third lens L₃ is a positivemeniscus lens having a convex surface facing the magnification side. Thesecond lens group G₂ is composed of fourth lens L₄ and fifth lens L₅.The fourth lens L₄ is a double concave lens, and the fifth lens L₅ is adouble convex lens. The third lens group G₃ is composed of sixth lensL₆, which is a plano-convex lens having a convex surface facing themagnification side.

Further, a wide space (sufficiently long distance) is maintained betweenthe second lens group G₂ and the third lens group G₃, and a colorcombination prism (or a ray separation prism) 2 is arranged in the spacebetween the second lens group G₂ and the third lens group G₃. The spacebetween the second lens group G₂ and the third lens group G₃ is set soas to satisfy the range defined by the formula (1). Specifically, thevalue of d₂₃/f₃ is 0.43 in Example 1.

Further, both surfaces of the first lens L₁ in Example 1 are asphericsurfaces represented by the aforementioned aspheric surface equation(Equation 1).

Table 1 shows data about Example 1. Table 1 shows the curvature radius Rof each lens surface (normalized by assuming the focal length of theentire lens system to be 1.00; same in the following tables), the centerthickness D of each lens and air space D between lenses (normalized in amanner similar to the curvature radius R, same in the following tables),and refractive index N_(d) and Abbe number ν_(d) of each lens ford-line. In Table 1, and Tables 3, 5, 7, 9 and 11, which will bedescribed later, surface numbers for each sign R, D, N_(d), and ν_(d)sequentially increase from the magnification side.

Further, at the top of Table 1, and Tables 3, 5, 7, 9 and 11, which willbe described later, focal length f of the entire system, half angle ω ofview, and FNo (f-number) are shown.

As described above, both surfaces of the first lens L₁ are aspheric.Table 2 shows aspheric coefficients K, A₃, A₄, A₅, A₆, A₇, A₈, A₉, A₁₀,A₁₁, and A₁₂ in the equation representing the aspheric surfaces forthese aspheric surfaces.

TABLE 1 f: 1.00, HALF ANGLE OF VIEW ω: 22.9°, FNo.: 1.97 SURFACECURVATURE DISTANCE REFRACTIVE ABBE NUMBER RADIUS R D INDEX N_(d) NUMBERν_(d) OBJ ∞ 71.921  1* −0.447  0.234 1.510100 56.2  2*  9.095  0.054  3 0.942  0.221 1.800000 48.0  4 −0.962  0.014  5  0.530  0.147 1.80000048.0  6  0.708  0.106  7 −0.938  0.054 1.846700 23.8  8  0.734  0.062  912.068  0.170 1.724000 55.3 10 −0.663  0.108 11 ∞  0.806 1.516300 64.112 ∞  0.072 13  1.327  0.180 1.806100 40.9 14 ∞  0.060 15 ∞  0.1081.516300 64.1 16 ∞  0.000 *ASPHERIC SURFACE

TABLE 2 ASPHERIC COEFFICIENT SURFACE NUMBER K A₃ A₄ A₅ A₆ 1 1.000000.00000E+00 6.04753E+00 −4.78664E+00 −6.07153E+00 2 1.00000 0.00000E+003.71334E+00   1.83536E−01 −1.29130E+01 A₇ A₈ A₉ A₁₀ A₁₁ A₁₂ 1  4.48877E−01 2.01341E+01 2.03388E+01   1.34286E+02 0.00000E+000.00000E+00 2 −1.05036E+01 5.31486E+01 1.20340E+02 −2.73790E+020.00000E+00 0.00000E+00

Further, FIG. 7-i through 7-iv are diagrams illustrating aberrations inExample 1. FIG. 7-i illustrates spherical aberration in Example 1, andFIG. 7-ii illustrates astigmatism in Example 1, and FIG. 7-iiiillustrates distortion in Example 1, and FIG. 7-iv illustrates lateralchromatic aberration in Example 1 (72.0 times magnification). In FIG.7-i, and FIGS. 8-i, 9-i, 10-i, 11-i and 12-i, which will be describedlater, spherical aberrations for d-line, F-line and C-line areillustrated. In FIG. 7-ii, and FIGS. 8-ii, 9-ii, 10-ii, 11-ii and 12-ii,which will be described later, aberrations (astigmatism) with respect tosagittal image planes and aberrations with respect to tangential imageplanes are illustrated. In FIG. 7-iv, and FIGS. 8-iv, 9-iv, 10-iv, 11-ivand 12-iv, which will be described later, lateral chromatic aberrationsof F-line and C-line with respect to d-line are illustrated.

As FIG. 7-i through 7-iv clearly illustrate, each aberration iscorrected in an excellent manner in the projection lens of Example 1.

Further, as Table 13 shows, the projection lens of Example 1 satisfiesthe formulas (1) through (7), formulas (1′) through (7′) and formulas(2″), (6″) and (7″).

Example 2

FIG. 2 is a schematic diagram illustrating the structure of a projectionlens in Example 2. The projection lens in Example 2 is structured in asubstantially similar manner to Example 1. However, in the projectionlens of Example 2, both surfaces of the third lens L₃ in the first lensgroup G₁ are aspheric, and the third lens L₃ is made of plastic.Further, in the projection lens of Example 2, the fifth lens L₅ in thesecond lens group G₂ is a positive meniscus lens having a convex surfacefacing the reduction side of the projection lens.

Further, in the projection lens of Example 2, a wide space is maintainedbetween the second lens group G₂ and the third lens group G₃, and acolor combination prism (or a ray separation prism) 2 is arranged in thespace between the second lens group G₂ and the third lens group G₃. Thespace between the second lens group G₂ and the third lens group G₃ isset so as to satisfy the range defined by the formula (1). Specifically,the value of d₂₃/f₃ is 0.43 in Example 2.

Table 3 shows data about Example 2. Table 3 shows the curvature radius Rof each lens surface, the center thickness D of each lens and air spaceD between lenses, and refractive index N_(d) and Abbe number ν_(d) ofeach lens for d-line.

As described above, both surfaces of the first lens L₁ and both surfacesof the third lens L₃ are aspheric. Table 4 shows aspheric coefficientsK, A₃, A₄, A₅, A₆, A₇, A₈, A₉, A₁₀, A₁₁, and A₁₂ in the equationrepresenting aspheric surfaces for these aspheric surfaces.

TABLE 3 f: 1.00, HALF ANGLE OF VIEW ω: 22.9°, FNo.: 1.94 SURFACECURVATURE DISTANCE REFRACTIVE ABBE NUMBER RADIUS R D INDEX N_(d) NUMBERν_(d) OBJ ∞ 71.970  1*  −0.378  0.113 1.510100 56.2  2*  1.051  0.055  3 0.961  0.231 1.772500 49.6  4  −0.873  0.014  5*  0.395  0.231 1.51010056.2  6*  1.111  0.107  7  −1.199  0.054 1.846700 23.8  8  0.758  0.065 9 −40.493  0.170 1.713000 53.9 10  −0.649  0.113 11 ∞  0.806 1.51630064.1 12 ∞  0.072 13  1.345  0.180 1.806100 40.9 14 ∞  0.065 15 ∞  0.1081.516300 64.1 16 ∞  0.000 *ASPHERIC SURFACE

TABLE 4 ASPHERIC COEFFICIENT SURFACE NUMBER K A₃ A₄ A₅ A₆ 1 1.000000.00000E+00 8.90517E+00 −7.02839E+00   −2.94483E+01 2 1.000000.00000E+00 2.19881E+00 3.82460E+00 −3.10533E+01 5 1.00000 0.00000E+00−1.92764E+00   0.00000E+00 −1.93526E−01 6 1.00000 0.00000E+008.85900E−01 0.00000E+00   3.60196E+00 A₇ A₈ A₀ A₁₀ A₁₁ A₁₂ 1 8.62994E+016.80710E+01 −6.14184E+02   1.59187E+03 0.00000E+00 0.00000E+00 26.51130E+00 1.50600E+02 4.15040E+01 −5.63815E+02   0.00000E+000.00000E+00 5 0.00000E+00 9.26357E+00 0.00000E+00 −1.55993E+02  0.00000E+00 0.00000E+00 6 0.00000E+00 −5.96285E+01   0.00000E+001.59689E+03 0.00000E+00 0.00000E+00

Further, FIG. 8-i through 8-iv are diagrams illustrating aberrations inExample 2. FIG. 8-i illustrates spherical aberration in Example 2, andFIG. 8-ii illustrates astigmatism in Example 2, and FIG. 8-iiiillustrates distortion in Example 2, and FIG. 8-iv illustrates lateralchromatic aberration in Example 2 (72.0 times magnification).

As FIG. 8-i through 8-iv clearly illustrate, each aberration iscorrected in an excellent manner in the projection lens of Example 2.

Further, as Table 13 shows, the projection lens in Example 2 satisfiesthe formulas (1) through (7), formulas (1′) through (7′) and formulas(2″), (6″) and (7″).

Example 3

FIG. 3 is a schematic diagram illustrating the structure of a projectionlens in Example 3. The projection lens in Example 3 is structured in asimilar manner to Example 1. However, Example 3 greatly differs fromExample 1 in that the projection lens of Example 3 is composed of fivelenses. Specifically, the projection lens of Example 3 is composed offirst lens group G₁, second lens group G₂ and third lens group G₃, whichare sequentially arranged from the magnification side. The first lensgroup G₁ is composed of first lens L₁ and second lens L₂, which aresequentially arranged from the magnification side. Both surfaces of thefirst lens L₁ are aspheric, and the first lens L₁ is made of plastic(negative meniscus lens shape having a concave surface facing themagnification side in the vicinity of the optical axis). Both surfacesof the second lens L₂ are aspheric, and the second lens L₂ is made ofplastic (double convex lens shape in the vicinity of the optical axis).Further, the second lens group G₂ is composed of third lens L₃ andfourth lens L₄, which are sequentially arranged from the magnificationside. The third lens L₃ is a double concave lens, and the fourth lens L₄is a positive meniscus lens having a convex surface facing the reductionside. The third lens group G₃ is composed of fifth lens L₅, which is aplano-convex lens having a convex surface facing the magnification side.

Further, in the projection lens of Example 3, a wide space is maintainedbetween the second lens group G₂ and the third lens group G₃, and acolor combination prism (or a ray separation prism) 2 is arranged in thespace between the second lens group G₂ and the third lens group G₃. Thespace between the second lens group G₂ and the third lens group G₃ isset so as to satisfy the range defined by the formula (1). Specifically,the value of d₂₃/f₃ is 0.46 in Example 3.

Table 5 shows data about Example 3. Table 5 shows the curvature radius Rof each lens surface, the center thickness D of each lens and air spaceD between lenses, and refractive index N_(d) and Abbe number ν_(d) ofeach lens for d-line.

As described above, both surfaces of the first lens L₁ and both surfacesof the second lens L₂ are aspheric. Table 6 shows aspheric coefficientsK, A₃, A₄, A₅, A₆, A₇, A₈, A₉, A₁₀, A₁₁, and A₁₂ in the equationrepresenting the aspheric surfaces for these aspheric surfaces.

TABLE 5 f: 1.00, HALF ANGLE OF VIEW ω: 22.8°, FNo.: 2.20 SURFACECURVATURE DISTANCE REFRACTIVE ABBE NUMBER RADIUS R D INDEX N_(d) NUMBERν_(d) OBJ ∞ 72.008  1* −0.302  0.209 1.510100 56.2  2* −0.795  0.014  3* 0.382  0.306 1.806100 40.9  4* −1.523  0.052  5 −0.546  0.054 1.84670023.8  6  0.683  0.057  7 −4.696  0.151 1.713000 53.9  8 −0.566  0.108  9∞  0.806 1.516300 64.1 10 ∞  0.072 11  1.236  0.180 1.806100 40.9 12 ∞ 0.058 13 ∞  0.108 1.516300 64.1 14 ∞  0.000 *ASPHERIC SURFACE

TABLE 6 ASPHERIC COEFFICIENT SURFACE NUMBER K A₃ A₄ A₅ A₆ 1 1.000000.00000E+00 1.68585E+01 1.54368E+01 −3.61587E+02 2 1.00000 0.00000E+00−2.68958E+00   2.12197E+01 −2.62487E+01 3 1.00000 0.00000E+00−6.17589E+00   0.00000E+00   7.65939E+01 4 1.00000 0.00000E+001.21943E−01 0.00000E+00 −6.68992E+01 A₇ A₈ A₉ A₁₀ A₁₁ A₁₂ 1 7.91372E+02  2.60019E+03 −2.09846E+03 −2.59005E+04 −6.23954E+04 3.60917E+05 27.76742E+00 −1.54717E+02 −7.33772E+02   3.06293E+03   7.63888E+03−2.13085E+04   3 −4.34110E+01   −6.50042E+02 −1.69836E+02   3.23284E+03  6.44907E+03 −1.48743E+04   4 4.31462E+02 −1.42259E+02 −8.62794E+02−5.01745E+03 −4.53965E+04 2.14070E+05

Further, FIG. 9-i through 9-iv are diagrams illustrating aberrations inExample 3. FIG. 9-i illustrates spherical aberration in Example 3, andFIG. 9-ii illustrates astigmatism in Example 3, and FIG. 9-iiiillustrates distortion in Example 3, and FIG. 9-iv illustrates lateralchromatic aberration in Example 3 (72.0 times magnification).

As FIG. 9-i through 9-iv clearly illustrate, each aberration iscorrected in an excellent manner in the projection lens of Example 3.

Further, as Table 13 shows, the projection lens in Example 3 satisfiesthe formulas (1) through (7), formulas (1′) through (7′) and formulas(6″) and (7″).

Example 4

FIG. 4 is a schematic diagram illustrating the structure of a projectionlens in Example 4. The projection lens in Example 4 is structured in asubstantially similar manner to Example 1. However, Example 4 mainlydiffers from Example 1 in that both surfaces of the third lens L₃ in thefirst lens group G₁ are aspheric, and the third lens L₃ is made ofplastic (positive meniscus lens shape having a convex surface facing themagnification side in the vicinity of the optical axis).

Further, a wide space is maintained between the second lens group G₂ andthe third lens group G₃, and a color combination prism (or a rayseparation prism) 2 is arranged in the space between the second lensgroup G₂ and the third lens group G₃. The space between the second lensgroup G₂ and the third lens group G₃ is set so as to satisfy the rangedefined by the formula (1). Specifically, the value of d₂₃/f₃ is 0.49 inExample 4.

Table 7 shows data about Example 4. Table 7 shows the curvature radius Rof each lens surface, the center thickness D of each lens and air spaceD between lenses, and refractive index N_(d) and Abbe number ν_(d) ofeach lens for d-line.

As described above, both surfaces of the first lens L₁ and both surfacesof the third lens L₃ are aspheric. Table 8 shows aspheric coefficientsK, A₃/A₄, A₅, A₆, A₇, A₈, A₉, A₁₀, A₁₁, and A₁₂ in the equationrepresenting aspheric surfaces for these aspheric surfaces.

TABLE 7 f: 1.00, HALF ANGLE OF VIEW ω: 22.9°, FNo.: 2.20 SURFACECURVATURE DISTANCE REFRACTIVE ABBE NUMBER RADIUS R D INDEX N_(d) NUMBERν_(d) OBJ ∞ 71.968  1* −0.395  0.086 1.510100 56.2  2*  0.692  0.061  3 0.719  0.215 1.772500 49.6  4 −1.586  0.014  5*  0.393  0.235 1.69350053.2  6*  1.255  0.097  7 −1.020  0.054 1.846700 23.8  8  0.704  0.046 9  3.212  0.158 1.713000 53.9 10 −0.751  0.108 11 ∞  0.806 1.51630064.1 12 ∞  0.072 13  1.176  0.180 1.806100 40.9 14 ∞  0.062 15 ∞  0.1081.516300 64.1 16 ∞  0.000 *ASPHERIC SURFACE

TABLE 8 ASPHERIC COEFFICIENT SURFACE NUMBER K A₃ A₄ A₅ A₆ 1 1.000000.00000E+00 4.06983E+00 1.62605E+01 −7.52623E+01   2 1.00000 0.00000E+00−3.96289E+00   1.39482E+01 1.30803E+01 5 1.00000 0.00000E+00−2.41100E+00   0.00000E+00 2.57974E+00 6 1.00000 0.00000E+00 2.23771E+000.00000E+00 2.21007E+00 A₇ A₈ A₉ A₁₀ A₁₁ A₁₂ 1 1.58200E+02 9.38801E+01−1.57833E+03   3.12054E+03 0.00000E+00 0.00000E+00 2 −6.85039E+01  −8.43208E+01   −2.99084E+01   8.15941E+02 0.00000E+00 0.00000E+00 50.00000E+00 5.16956E+01 0.00000E+00 −6.40602E+02   0.00000E+000.00000E+00 6 0.00000E+00 1.24166E+02 0.00000E+00 5.80033E+020.00000E+00 0.00000E+00

Further, FIG. 10-i through 10-iv are diagrams illustrating aberrationsin Example 4. FIG. 10-i illustrates spherical aberration in Example 4,and FIG. 10-ii illustrates astigmatism in Example 4, and FIG. 10-iiiillustrates distortion in Example 4, and FIG. 10-iv illustrates lateralchromatic aberration in Example 4 (72.0 times magnification). As FIG.10-i through 10-iv clearly illustrate, each aberration is corrected inan excellent manner in the projection lens of Example 4.

Further, as Table 13 shows, the projection lens in Example 4 satisfiesthe formulas (1) through (7), formulas (1′) through (7′) and formulas(2″), (6″) and (7″).

Example 5

FIG. 5 is a schematic diagram illustrating the structure of a projectionlens in Example 5. The projection lens in Example 5 is structured in asubstantially similar manner to Example 2. However, Example 5 differsfrom Example 2 in that a stop 3 (a mask may be provided instead of thestop) is provided on the magnification side of the first lens L₁.

Further, a wide space is maintained between the second lens group G₂ andthe third lens group G₃, and a color combination prism (or a rayseparation prism) 2 is arranged in the space between the second lensgroup G₂ and the third lens group G₃. The space between the second lensgroup G₂ and the third lens group G₃ is set so as to satisfy the rangedefined by the formula (1). Specifically, the value of d₂₃/f₃ is 0.50 inExample 5.

Table 9 shows data about Example 5. Table 9 shows the curvature radius Rof each lens surface, the center thickness D of each lens and air spaceD between lenses, and refractive index N_(d) and Abbe number ν_(d) ofeach lens for d-line. As described above, both surfaces of the firstlens L₁ and both surfaces of the third lens L₃ are aspheric. Table 10shows aspheric coefficients K, A₃, A₄, A₅, A₆, A₇, A₈, A₉, A₁₀, A₁₁, andA₁₂ in the equation representing aspheric surfaces for these asphericsurfaces.

TABLE 9 f: 1.00, HALF ANGLE OF VIEW ω: 17.8°, FNo.: 2.20 SURFACECURVATURE DISTANCE REFRACTIVE ABBE NUMBER RADIUS R D INDEX N_(d) NUMBERν_(d) OBJ ∞ 72.0303  1 (STOP) ∞  0.100  2*  −0.368  0.079 1.510100 56.2 3*  0.729  0.045  4  0.746  0.186 1.772500 49.6  5  −1.050  0.014  6* 0.360  0.195 1.693500 53.2  7*  0.775  0.101  8  −0.775  0.054 1.84670023.8  9  0.864  0.040 10 −31.396  0.143 1.713000 53.9 11  −0.595  0.10812 ∞  0.807 1.516300 64.1 13 ∞  0.072 14  1.146  0.180 1.806100 40.9 15∞  0.064 16 ∞  0.108 1.516300 64.1 17 ∞  0.000 *ASPHERIC SURFACE

TABLE 10 ASPHERIC COEFFICIENT SURFACE NUMBER K A₃ A₄ A₅ A₆ 2 1.000000.00000E+00 4.86139E+00 1.84013E+01 −7.80155E+01   3 1.00000 0.00000E+00−4.54589E+00   1.63763E+01 2.08185E+01 6 1.00000 0.00000E+00−2.85002E+00   0.00000E+00 9.60284E+00 7 1.00000 0.00000E+00 2.74349E+000.00000E+00 1.98322E+01 A₇ A₈ A₉ A₁₀ A₁₁ A₁₂ 2 1.52393E+02 5.81402E+01−1.61795E+03   3.99994E+03 0.00000E+00 0.00000E+00 3 −7.77149E+01  −1.54453E+02   −1.34723E+02   1.44825E+03 0.00000E+00 0.00000E+00 60.00000E+00 1.41061E+00 0.00000E+00 −3.05437E+02   0.00000E+000.00000E+00 7 0.00000E+00 −1.02770E+02   0.00000E+00 5.92258E+030.00000E+00 0.00000E+00

Further, FIG. 11-i through 11-iv are diagrams illustrating aberrationsin Example 5. FIG. 11-i illustrates spherical aberration in Example 5,and FIG. 11-ii illustrates astigmatism in Example 5, and FIG. 11-iiiillustrates distortion in Example 5, and FIG. 11-iv illustrates lateralchromatic aberration in Example 5 (72.0 times magnification). As FIG.11-i through 11-iv clearly illustrate, each aberration is corrected inan excellent manner in the projection lens of Example 5.

Further, as Table 13 shows, the projection lens in Example 5 satisfiesthe formulas (1) through (7), formulas (1′) through (7′) and formulas(2″), (6″) and (7″).

Example 6

FIG. 6 is a schematic diagram illustrating the structure of a projectionlens in Example 6. The projection lens in Example 6 is composed of fivelenses in a manner similar to Example 3. However, Example 6 mainlydiffers from Example 3 in that both surfaces of the fourth lens L₄ inthe second lens group G₂ are aspheric, and the fourth lens L₄ is made ofplastic (double convex lens shape in the vicinity of the optical axis),and that an optical prism is not arranged between the second lens groupG₂ and the third lens group G₃. In Example 5, an optical prism forseparating/combining rays may be inserted between the second lens groupG₂ and the third lens group G₃. Alternatively, a reflection mirror (2 d)for separating rays may be arranged, as illustrated in FIG. 16.

Further, the space between the second lens group G₂ and the third lensgroup G₃ is set so as to satisfy the range defined by the formula (1).Specifically, the value of d₂₃/f₃ is 0.52 in Example 6.

Table 11 shows data about Example 6. Table 11 shows the curvature radiusR of each lens surface, the center thickness D of each lens and airspace D between lenses, and refractive index N_(d) and Abbe number ν_(d)of each lens for d-line.

As described above, both surfaces of the first lens L₁ and both surfacesof the second lens L₂ and both surfaces of the fourth lens L₄ areaspheric. Table 12 shows aspheric coefficients K, A₄, A₅, A₆, A₇, A₈,A₉, A₁₀, A₁₁, and A₁₂ in the equation representing aspheric surfaces forthese aspheric surfaces.

TABLE 11 f: 1.00, HALF ANGLE OF VIEW ω: 25.1°, FNo.: 2.20 SURFACECURVATURE DISTANCE REFRACTIVE ABBE NUMBER RADIUS R D INDEX N_(d) NUMBERν_(d) OBJ ∞ 79.822  1* −0.331  0.239 1.510100 56.2  2* −6.056  0.042  3* 0.419  0.406 1.834800 42.7  4* −1.048  0.051  5 −0.512  0.060 1.80520025.4  6  0.872  0.030  7*  3.496  0.184 1.772500 49.6  8* −0.742  0.838 9  1.353  0.200 1.834800 42.7 10 ∞  0.066 11 ∞  0.120 1.516300 64.1 12∞  0.000 *ASPHERIC SURFACE

TABLE 12 ASPHERIC COEFFICIENT SURFACE NUMBER K A₃ A₄ A₅ A₆ 1 1.000000.00000E+00 1.28674E+01 1.70656E+01 −2.29450E+02   2 1.00000 0.00000E+00−2.26619E+00   1.90305E+01 −3.50701E+01   3 1.00000 0.00000E+00−5.36574E+00   0.00000E+00 5.71369E+01 4 1.00000 0.00000E+00−3.20053E−01   0.00000E+00 9.59539E+00 7 1.00000 0.00000E+00 2.96324E+000.00000E+00 1.08356E+01 8 1.00000 0.00000E+00 2.02274E+00 0.00000E+002.64986E+00 A₇ A₈ A₉ A₁₀ A₁₁ A₁₂ 1 4.16384E+02 1.27361E+03 −7.60099E+02−1.04046E+04 −2.64514E+04   1.30506E+05 2 8.32473E+01 5.98553E+01−8.54003E+02 −1.10198E+03 2.24827E+03 1.15377E+04 3 −4.64922E+01  −3.63889E+02     2.33018E+01   1.67068E+03 1.98668E+03 −7.75967E+03   49.53505E+01 −5.60177E+02   −4.76271E+00   4.21821E+03 −3.80502E+03  −1.00132E+04   7 1.01738E+02 −4.06136E+01   −1.35470E+03 −1.47497E+031.74072E+04 −2.00369E+04   8 9.68716E+00 2.80400E+02   5.94351E+02−2.23248E+03 −1.18042E+04   4.04111E+04

Further, FIG. 12-i through 12-iv are diagrams illustrating aberrationsin Example 6. FIG. 12-i illustrates spherical aberration in Example 6,and FIG. 12-ii illustrates astigmatism in Example 6, and FIG. 12-iiiillustrates distortion in Example 6, and FIG. 12-iv illustrates lateralchromatic aberration in Example 6 (72.0 times magnification).

As FIG. 12-i through 12-iv clearly illustrate, each aberration iscorrected in an excellent manner in the projection lens of Example 6.

Further, as Table 13 shows, the projection lens in Example 5 satisfiesthe formulas (1) through (7), formulas (1′) through (7′) and formulas(6″) and (7″).

TABLE 13 (1), (1′) (2), (2′), (2″) (3), (3′) (4), (4′) (5), (5′) (6),(6′), (6″) (7), (7′), (7″) d₂₃/f₃ | D₁₂/ff | bf/f₃ f₃/f D₁₂/f₃ f₁/f f₂/fEXAMPLE 1 0.43 32.90 0.08 1.65 0.70 0.62 −1.85 EXAMPLE 2 0.43 35.00 0.081.67 0.69 0.67 −2.44 EXAMPLE 3 0.46 20.80 0.08 1.53 0.76 0.45 −0.85EXAMPLE 4 0.49 40.60 0.09 1.46 0.81 0.63 −1.69 EXAMPLE 5 0.50 236.80 0.10 1.42 0.83 0.64 −1.73 EXAMPLE 6 0.52 24.50 0.09 1.62 0.73 0.50 −1.15

The projection optical system (projection lens) of the present inventionand a projection-type display apparatus using the projection opticalsystem of the present invention are not limited to the aforementionedexamples. Various modifications are possible without departing from thegist of the present invention. For example, the shape of each lens, thenumber of lenses constituting each lens group, the position ofarrangement of each lens may be set in an appropriate manner.

What is claimed is:
 1. A projection lens comprising: a first lens grouphaving positive refractive power; a second lens group having negativerefractive power; and a third lens group having positive refractivepower, which are sequentially arranged from the magnification side ofthe projection lens, wherein the reduction side of the projection lensis telecentric, and wherein the following formulas (1) and (2) aresatisfied:0.30≦d ₂₃ /f ₃≦0.65  (1); and10≦|D ₁₂ /ff|  (2), where d₂₃: space in air between the second lensgroup and the third lens group, f₃: focal length of the third lensgroup, D₁₂: total length of the first lens group and the second lensgroup in the direction of an optical axis, and ff: length from the mostmagnification-side surface in the entire system of the projection lensto a magnification-side focus point of the entire system of theprojection lens.
 2. A projection lens, as defined in claim 1, whereinthe following formula (3) is satisfied:bf/f ₃≦0.2  (3), where bf: back focus in air of the entire system.
 3. Aprojection lens, as defined in claim 1, wherein the following formula(4) is satisfied:1.2≦f ₃ /f≦1.9  (4), where f: focal length of the entire system.
 4. Aprojection lens, as defined in claim 1, wherein the following formula(5) is satisfied:0.4≦D ₁₂ /f ₃≦1.1  (5).
 5. A projection lens, as defined in claim 1,wherein the following formula (6) is satisfied:0.2≦f ₁ /f≦1.0  (6), where f₁: focal length of the first lens group f:focal length of the entire system.
 6. A projection lens, as defined inclaim 1, wherein the following formula (7) is satisfied:−3.5≦f ₂ /f≦−0.5  (7), where f₂: focal length of the second lens groupf: focal length of the entire system.
 7. A projection lens, as definedin claim 1, wherein the first lens group is composed of a negative lens,a positive lens and a positive lens, which are sequentially arrangedfrom the magnification side of the projection lens.
 8. A projectionlens, as defined in claim 1, wherein the first lens group is composed ofa negative lens and a positive lens, which are sequentially arrangedfrom the magnification side of the projection lens.
 9. A projectionlens, as defined in claim 7, wherein the second lens group is composedof a negative lens and a positive lens, which are sequentially arrangedfrom the magnification side of the projection lens.
 10. A projectionlens, as defined in claim 8, wherein the second lens group is composedof a negative lens and a positive lens, which are sequentially arrangedfrom the magnification side of the projection lens.
 11. A projectionlens, as defined in claim 9, wherein the third lens group consists of apositive lens.
 12. A projection lens, as defined in claim 10, whereinthe third lens group consists of a positive lens.
 13. A projection lens,as defined in claim 1, wherein illumination light and projection lightare separated from each other in an area between the second lens groupand the third lens group.
 14. A projection lens, as defined in claim 1,wherein rays from a plurality of light valves are combined together inan area between the second lens group and the third lens group.
 15. Aprojection lens, as defined in claim 1, wherein a aperture stop isarranged on the magnification side of the first lens group.
 16. Aprojection-type display apparatus comprising: a light source; a lightvalve; an illumination optical unit that guides rays of light from thelight source to the light valve; and a projection lens, as defined inclaim 1, wherein the rays of light from the light source are opticallymodulated by the light valve and projected onto a screen by theprojection lens.